I have a large two story home that I use Xfinity zigbee contacts on every window running on an edge driver. I have 27 of these contacts currently. My v2 Smartthings hub works well for the first floor and I have had no drop outs on that floor, but I have constant drop outs on the top story in four different rooms. I have 8 zigbee repeaters through out the house. I was hoping that would keep this from happening. I was thinking of adding a new Aeotec v3 hub on the second story to add the contacts to. I would hardwire that hub. In you guy’s opinions, would this help, or is that more of an issue? This morning the alarm went off early in the morning when a contact came back on. It appears it showed offline, then open, the closed. So it set off the alarm.
I would not do that. You have a repeater/interference issue. Adding a second hub would be nightmarish in terms of management of automations, scenes, and anything else you’d want to do for ease of use to control/manage your home. Either add a new wall switch, outlet, or even a Centralite 3-Series Night Light (zigbee 1.2 repeater only). You should also check to see what Zigbee channel your hub is on ad what wifi channel your router is using.
This.
Figure out why your repeater mesh isn’t stretching to the second floor and fix that.
Both John and Nathan have given you the usual best practices advice, which is to add more repeaters rather than a second hub, but first let’s drill a little deeper into the specifics of your situation, just in case you are in one of the unusual categories. 
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what is the material composition of your home? Is it adobe or cement? Or do you have radiant floor heating with water pipes running through the floors? In any of these three cases, people do often find it difficult to get signal from one floor to another, and there have been a few members who had to put a hub on each floor to handle this kind of set up. In some parts of the world, including parts of New Mexico and Vietnam, stucco, cement, or Adobe are pretty common building materials, so the usual best practices might not apply. If it’s an older house, even if the walls are wood or plaster, they might have chicken wire lathing or metal backed insulation, and that can also create signal transmission issues. Foil wallpaper can also be a problem.
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normally eight repeaters should be enough to handle 27 sensors, but you could be cutting it close depending on the exact physical location. A typical inexpensive Zigbee smart plug, for example, can usually parent 3 to 5 children. Some can only handle two, though. And it’s usually hard to find this information except by trial and error, the manufacturers don’t make a big deal out of it.
So what are the brand and models of each of the repeating devices and where exactly are they relative to the sensors? Ideally we would want three or four sensors within 30 feet or so of each repeater. Remember that these are Omni directional devices, so it’s fine for a repeater to be 10 feet down from a sensor on the next floor, again, as long as we aren’t running into materials issues as I mentioned in point one.
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what country are you in? The US allows for the use of “boosted Zigbee” which has a stronger transmission signal, but many other countries, including all of the EU, don’t allow for the boost so all the Zigbee devices, including the hubs, have lower transmission strength, which again might call for more repeaters.
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where exactly is the Hub physically located? If it’s in a cabinet, for example, or if it’s too close to the Wi-Fi router, that could be blocking signal in one direction. which might make it hard for the signal to get through to the floors above. Also, if it’s in an attached garage with an insulated roof, that can be a problem for devices on the floors above.
Well, that should be enough to start. Since you’re getting good signal lower down, it sounds like a mesh issue, we just need to know the specifics to figure out what the best steps will be.
Technical note: everything said above applies only to Zigbee, not zwave, which has a different parenting structure. I just didn’t want to confuse anybody, we’re pretty deep into the technical stuff here.
While an extra hub may well do the job, it is only something I would recommend when there is an obvious logical separation you can exploit. Once you start automating across hubs you lose the potential for local execution, something you probably wouldn’t want if you have a single alarm. I’d want to know why ZigBee routing isn’t doing the job for you before I took that step.
Thanks guys for all the feedback. I will post the schematic/ layout of the house and repeaters. I’ll also list the makes of the zigbee outlets being used as repeaters. This house was originally built in 1927 so there is a ton of wood between floors. Shiplap and then sheetrock. The limit per repeater makes sense here. Some rooms have up to 5 windows each. Only 1 or 2 windows per room are dropping. Out of 27 contacts, 16 are upstairs. I will also look to more centralize my hub. Right now it is against an outer wall of the living room, and there is an Orbi Mesh Satellite router right next to it.
Wood, shiplap, and sheetrock shouldn’t be a problem, although if it’s really thick you might have a slight signal drop off.
The fact that some sensors in the room are fine and others are not does sound like it’s probably just not enough child slots on the available repeaters. Although it could be that one side of the room has less signal than the other, it can happen particularly if the issue is interference with local Wi-Fi. (I’ve previously told the story here of when I added a plug-inWi-Fi booster to a room and when I put it on one side all my Zigbee devices to the east of it went off-line, but if I just moved it to a 90° wall, everything was happy. )
Anyway, do let us know the brand and model of the repeating devices and that should give us a better idea 
I have 8 of these. They state that they are also repeaters, but it doesn’t say how many at a time they can host. I can add a couple zigbee wall switches upstairs also. Is the Leviton zigbee switch a good choice? I have a ton of leviton wifi switches, but no zigbees.
Was this happening before the June 2022 upgrade?
Not that I noticed. I just started running those on the alarm system. That’s when I noticed it. LOUDLY. lol
UPDATE I move my hub to a central spot on the first floor. Didn’t notice much difference. Added two more repeaters upstairs. I had to actually remove the offline sensors and re-add them. Then they showed all online. Last night three different upstairs sensors went offline. Would there be a need to remove and re-add each to reset their “route”?
You don’t need to remove and re-add each sensor, but you do need to get them to reset their routes before they will consider the new repeaters as possible parents.
To do that, you do a “zigbee heal“ by taking the hub off power but leaving everything else on power. Leave the hub off power for about 20 minutes. All of the other devices will go into “panic mode“ because they can’t find the hub. Then after you put the hub back on power, they will all rebuild their routes, so they will be able to start using the new repeater if it’s appropriate.
It can take a few hours before all of this gets finished, so most field techs don’t check it until the next day.
Thanks for the heads up. I’m still learning here. Great community support.
I’m still in the process of adding and moving things around to give an update. But I have another question related to this. In the old IDE when the device was on a stock DTH, you could click on the device and see the route. With the new edge drivers, is there a way to do that? I’m VERY new to the CLI and have not figured my way around yet.